(1)

select TO_CHAR(123.56,'999.9') from dual; will return 123.6

select TO_NUMBER('123.56','999.9') from dual; will fail because of error "ORA-01722: invalid number"

(2)

select TO_CHAR(123.56,'999') from dual; will return 124

select TO_NUMBER(123.56,'999') from dual; will fail because of error "ORA-01722: invalid number"

(3)

select TO_CHAR(123.56,'9999.99') from dual;will return 123.56

select TO_NUMBER('123.56','9999.99') from dual; will return 123.56

(4)

select TO_CHAR(123.56,'9999') from dual; will return 124

select TO_NUMBER('123.56','9999') from dual; will fail because of error "ORA-01722: invalid number"

(5)

select TO_CHAR(123.56,'99') from dual; will return ###

select TO_NUMBER(123.56,'99') from dual; will fail because of error "ORA-01722: invalid number"

(6)

select TO_CHAR(123.56,'999.99') from dual; will return 123.56

select TO_NUMBER(123.56,'999.99') from dual; will return 123.56